All I can say is hop as high and as hard as you can, and whip it with all your strength and after the 1st whip is underneath you, just quickly flick your wrists to complete the second whip and STOMP the mother fucking deck down. After practice they become almost as easy as single whips. Also learn them fly out first
Practice is the key, not much in the height of your hop but the speed you rotate it, try and pull your feet up to your ass......trust me that helped me out
jump as high as you can & flick your wrists hell hard. also concentrate on keeping your feet together this was my main problem when i was learning them